This invention relates to a control device having a thermostatic working element and a control element that can be actuated thereby.
Control devices of this type, as shown in German Patent DE-PS No. 24 44 931, have proven themselves in practice and are manufactured and used in large quantities. In the particular device shown in the German Patent, a one-piece metal housing is manufactured as a machined part having a cup-shaped receiving means for the thermally expandable material. The cup-shaped receiving means is closed by a rubber or elastic membrane held by a guide part which is also made of a machined metal part. The guide part is secured in the housing by a beaded edge. The housing is closed by a cover plate made of plastic which has a microswitch attached thereto and which, by means of a flanged edge, is held in the housing.
German Utility Model DE-AS No. 23 48 099 shows a similar control device constructed at least partially of plastic. In the case of this construction, a generally sleeve-shaped basic body made of plastic is provided into which a guide part for the working piston is inserted. A thermostatic working element constructed as an integral unit is then inserted from one side into the basic body. The integral unit consists of a metallic housing with an enclosed thermo-elastic material and a movable working piston provided with a seal. The working element snaps into the basic body by means of a clip arrangement. An end plate which carries a microswitch is inserted into the basic body from the other side. This end plate also snaps into the basic body by means of a clip arrangement. This type of device has not proven itself in practical applications, especially when the integrally constructed thermostatic working element is not held securely enough in the basic body. In addition, the manufacturing costs for this control device are relatively high.
An object of the present invention is to provide a control device of the initially mentioned type which may be manufactured at a greatly decreased cost.
These and other objects are attained in a thermostatic control device which comprises a primary housing, a movable working element extending through a wall of the primary housing, a secondary housing secured to the primary housing and containing a thermally expandable material, and an elastic membrane for retaining the expandable material in place. The primary housing has walls which define a tightly enclosed interior space for enclosing the control element. The movable working element extends through one of these walls and contacts with the control element. The secondary housing, which is fastened to the primary housing, is formed with a cup-shaped receiving means which contains the thermally expandable material. The secondary housing positions and holds the expandable material immediately adjacent to the end of the working element which extends through the exterior of the primary housing wall. An elastic membrane is provided between the expandable material and the working element. The elastic membrane is clamped between the primary housing and an interior surface of the secondary housing.
The secondary housing is preferably secured to the primary housing by plastically deforming an edge of the secondary housing around a shoulder which is integrally formed with the primary housing. For this reason, the secondary housing is preferably formed of metal, while the primary housing is preferably formed of plastic. The secondary housing is preferably a stamped sheet metal part. In another preferred embodiment, a fastening structure, such as external threads, is provided on the exterior of the secondary housing. The control device of the present invention may be utilized with a microswitch to form an electrical control device, or with a valve arrangement to form a hydraulic or pneumatic control device.
By means of this development, it is possible to manufacture the housing from less expensive and more easily machined materials than previously, so that significant savings can be achieved during manufacturing. These savings are very important since control devices of this type are used in very large quantities and a decrease in cost is an important advantage.
In a preferred embodiment of this invention, the secondary housing is constructed as a plastically deformed sheet-metal part. These sheet-metal parts may be manufactured very easily by deep-drawing, pressing, or stamping at low costs. In another embodiment of the invention, the secondary housing is provided with a fastening arrangement on its exterior surface. This provides for the secure fastening of the control device to other structures for extended periods of time.
In another preferred embodiment of the invention, the primary housing is manufactured in one piece with a guide part for the working element. In this embodiment, further simplification is achieved since the primary housing and the guide part can be simply manufactured as a molded plastic part. In the case of this embodiment, only an end plate and the secondary housing must be manufactured separately. The end plate, which is also preferably made of plastic, is connected to an edge of the primary housing by means of ultrasonic welding.
In yet another embodiment of the invention, the primary housing is manufactured in one piece with the end plate. In this embodiment, the guide part for the working piston is a separate structural part which, however, can also be manufactured easily as a molded plastic part. Assembly then becomes especially simple, with the guide part held between the primary and secondary housings. A separate fastening of the guide part will then not be required.